Transcripts from T1 infecting ordinary and lambda-preinfected cultures will be separated by gel electrophoresis, transferred by blotting to DBM paper, and hybridized to probes prepared from T1 DNA to study the size distribution of the T1-specific mRNA. Probes will include both total DNA from T1, and fragements obtained by restriction nuclease digestion and preparative gel electrophoresis. Bacterial strains harboring a plasmid into which lambda Q gene has been cloned, placing it under the control of Lac regulaiion, will be investigated as possible hosts for preliminary genetic and biochemical studies of Q-mediated exclusion.